Introduction:
There is a common defect that we find on many of our home surveys that can go unseen for long periods of time. It occurs under the roof at eaves level and often leads to other more serious defects occurring such as timber decay or even rainwater ingress to the property itself. The problem occurs due to incorrectly installed sarking felt or sarking felt that has deteriorated.
Understanding Sarking Felt:
Sarking felt is an underlay that is positioned beneath the tiles of a roof to provide a secondary defence against windblown rain. Sarking felt should be lapped into the gutter so that any rainwater that finds its way beneath the tiles can be safely drained away.
The Consequences of Incorrectly Installed or Deteriorated Sarking Felt:
If the sarking felt is incorrectly installed without correct support, it will ‘sag’ causing rainwater to collect and the leading edge of the felt to fall behind the gutter. This will allow rainwater to be channelled into the eaves construction resulting in decay and damage. The rainwater can sometimes also find its way into the internal walls of the building causing more damage to the fabric of the building.
A poorly specified sarking felt can also lead to water damage as it will quickly disintegrate to a point where it falls behind the gutter causing to water damage; as can be seen on the image above.
The Role of Proper Support and Flashing:
The remedy is to ensure that eaves sprockets, or better still continuous tilting fillets (please see image below) are incorporated under the sarking felt to provide support and prevent sagging.
In addition, a separate more durable flashing strip, such as a DPC (damp proof course), should be used where the underlay laps over the barge board and into the gutter.
The above two details may seem inconsequential in relation to the rest of the roof, however, their omission can lead to serious defects and should not be overlooked. It will be much more cost effective to check that they are fitted now rather than having to remedy their omission later.
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